Welcome, welcome, one and all, to the first of what will hopefully be a few memos on this board. The whole point of these things is to be bite-sized so I'll skip the whole ramble I would usually go on right now, long story short I want to help make fan characters better than they maybe could be.Disclaimer: my actual level of experience making fan characters isn't as developed as some people but I do at least figure I can offer a few pointers so take what I say with a grain of salt.

INTERESTS! They're something that every character has, and probably one of the easiest way to provide depth to a character. You can dress them up in fancy tags all you want, sorting them into Hogwarts houses and DnD alignments and such, but interests are where it's at. So I'm going to offer a bit of very specific advice when it comes to choosing interests for your character.

1.) MAKE THEM VARIED.
This one's probably the most obvious one. If you make your character too single-minded, it reeks of shallow one-dimensionality. I'm not exactly innocent of this particular tip myself, but it is something to be wary of. Equius is interested in robotics and fine art and also archery. None of those are connected. And yet nobody questions a thing.

A bit of a sub-tip, give them interests that have nothing to do with their theme. What does roleplaying have to do with being a Scorpio? Nothing! Since when does matchmaking play a role in being a Leo? I dunno. This helps the dimensionality problem, making them seem more like real people. If you're TOO random, be aware that it might seem lazily slapped together, so do keep their personality in mind, but do try and reach out a bit.

2.) DON'T MAKE YOUR CHARACTER GOOD AT ALL OF THEM.
John and Karkat SUCK at writing computer code. Tavros and Gamzee love slam poetry, but they suck at it. Jade can't play the flute. Jake's taste in movies is god-awful. But they like that stuff anyway. You probably aren't a complete expert on everything you love, but that doesn't stop you from enjoying it. Giving flaws to characters is a really good way to make them seem real and relatable, don't be afraid to give bad traits/qualities to them!

3.) INTERESTS CHANGE! CONSIDER PAST/FUTURE INTERESTS.
Jane used to be interested in gardening. Aradia used to be interested in archaeology before she died. Rose wasn't interested in knitting until John gave her a birthday present. People change over time, they have phases and their interests are fluid. You don't have to make a timeline or anything, but it's a fun exercise to have your characters remember embarrassing phases they had in their youth. Maybe they were obsessed with this one TV show, maybe they had a really favourite food, perhaps they've grown tired of bikes. People that aren't concrete are nice and solid.

I'm doing my best to keep this brief so I'll cap it off here, but feel free to add things on!

The tip about changing interests over time was good, the tip about not having too similar and too discrepant interests was solid but the tip about "liking =/= good at it" is GREAT!
Well done. Very well done.